GCEP Technical Progress Report April 2012 Project: Synthesis of Biofuels on Bioelectrodes

The proposed research explores the opportunities and bottlenecks of a novel approach for carbon-neutral synthesis of energy-dense transportation fuel from electrical energy (electrofuels). The technology is based on microbial CO2 fixation and biofuel production at cathodes in modified fuel cells by naturally occurring and genetically modified microbes. This approach takes advantage of known microbial enzymes, pathways, and organisms, but requires the engineering of novel pathways and communities for the production of biofuels as well as the engineering of the cathodic process. Biofuels encompasses a broadly defined class of relatively reduced gaseous or liquid organic molecules, and includes methane, ethane, long chain alcohols, oils, fatty acid esters, and isoprenes. While chemically diverse, they are biosynthetically typically derived from acetyl-CoA or related small molecule intermediates, with the exception of methane. For the purpose of this proposal and the limited scope that can be addressed in a three year research program, we will focus on synthesis of acetate, fatty acids, and surrogate compounds enable to study uptake of cathodic electons. However, because of the choice of experimental system including the specific microorganisms, the platform can be adopted to drive the autotrophic synthesis of isoprenes, methane, and other hydrocarbons that can be easily separated from the reactor and represent energy-dense biofuels. In the first approach, we have been exploring the use of well developed microbial organisms as platforms for metabolizing cathodic electrons. Using Cupriavidus necator we were able to demonstrate for the first time direct uptake and metabolism of electrons form cathodic surfaces. On the other hand, experiments using E. coli in conjunction with low redox potential electron shuttle compounds were not successful. Introduction Petroleum and other fossil hydrocarbons are primarily used as energy source for liquid (transportation) fuels as well as raw material for organic syntheses of commodity and fine chemicals. These uses represent the largest contribution to a net release of CO2 and global warming. Development of novel and alternative energy technologies to reduce or eliminate net CO2 release as well as to sustainably produce fuels and other organic compounds from electricity and CO2 are urgently needed but often limited by their incompatibility with the current liquid hydrocarbon-based infrastructure (e.g. H2 or electricity) in storage, transport, and use. Currently, solar and wind energy are the most promising sources for renewable energy, and, similarly as nuclear energy, produce electricity as the primary energy form. In the absence of better electricity and distribution technologies (e.g. battery), new approaches are needed to connect electrical energy to the infrastructure advantages of hydrocarbon fuels. This proposal explores ideas and proposes to test the bottlenecks of a new technology linking electricity to synthesis of fuels and other useful chemicals at cathodes using microorganisms. In the past year research has focused on exploring two microorganisms whose general metabolism and physiology has been studied extensively in the past: Cupriavidus necator, E. coli, and Shewnella oneidensis MR1.